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Fencing calculations
Before any fencing job is started it is important to calculate the quantity of materials required. The type and number of posts and stays, the length of wire and the number of gates and fittings should be accurately determined and purchases made if necessary. It is very frustrating to run out of posts or wire or be a gate fitting short before the job is finished.
The first step is to estimate or measure the length of the fence or perimeter of a paddock. This can be done by "stepping out" or pacing the fence line or using a tape measure. With practice pacing a fence line can become a quick and accurate method of determining the length.
Unless a paddock has an uneven shape it is not necessary to measure every side. The perimeter of paddocks with basic geometric shapes, such as squares and rectangles, can be calculated from one or two measurements. Even diagonal corners can be calculated. For revision on distance and perimeters go to the section on Measurement and calculation in Maths in the workplace in the unit RTC2801A Participate in workplace communications.
Another method for calculating the length of fence lines is to use a farm map. If the map is drawn to scale accurately a ruler can be used to measure the required distance on the map, which is then multiplied by the scale. Topographic maps, aerial photographs and satellite imagery can be used in the same manner. GPS systems can also be used to calculate distances.
All these methods are particularly useful in situations where walking along the fence line is not practical. Large properties and paddocks, difficult and steep terrain and fence lines running through thick vegetation all make on-the-ground measurements difficult.
If a map or photo is used to calculate the length of a fence line, an allowance needs to be made for the slope of the ground. The steeper the slope, the greater the actual distances compared with what is measured on the map.
Once the length of the fence line has been determined the materials can be calculated.
End assemblies - are required at the end of each line and at gateways, corners, wherever the fence changes direction, at the crest of hills and the bottom of gullies. In corners where two or more fence lines meet, the strainer post must be stayed for each fence. Thus a single strainer post may have two, three or even four stays. The concrete strainer post in the photo below has two concrete stays and one wooden stay.
Line posts – are set at regular intervals between the end assemblies. The number of line posts required in a single strain can be calculated as follows:
| No. of line posts = | (Distance between end assemblies) _____________________________ ( Interval between line posts ) |
- 1 |
Wire – the length of wire needed is calculated by multiplying the length of the strain by the number of wires. Extra wire is needed to wrap around the strainer posts at each end of the line. Allowing one metre at each end is usually sufficient. The number of coils of wire can be calculated from the total length needed.
Gate – numbers and placement are determined by the design and terrain of the paddock. The distance across each gateway must be taken off the length of the fence before calculating the number of line posts and length of wire.
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